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export files DPI means nothing

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Hi

 

i am confuse when i using the DPI setting.

 

I  want my file export have a high quality.

 

So i go to document setup to set the DPI  300 or 400.

 

But when i export file to jpg,png,tiff , the file still the same size.

 

please help me understand how this work

 

Thanks!

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DPI means nothing. It is the pixel dimension divided by desired print resolution that equals the effective PPI.

 

So say one wants an image to print at 300 dpi and occupy a 4" space, the inverse of the above is multiply 300 x 4" and therefore one needs an image of 1200 pixels wide to achieve an effective resolution of 300 dpi.

 

The DPI field is only an information field (i.e., it means nothing as regards quality) that can aid an application for opening/placing it initially. But all that matters is pixel dimensions and the above math.

 

Mike


My computer is a nothing-special Toshiba laptop with unremarkable specs running Windows 10 64-bit.

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DPI means nothing. It is the pixel dimension divided by desired print resolution that equals the effective PPI.

 

So say one wants an image to print at 300 dpi and occupy a 4" space, the inverse of the above is multiply 300 x 4" and therefore one needs an image of 1200 pixels wide to achieve an effective resolution of 300 dpi.

 

The DPI field is only an information field (i.e., it means nothing as regards quality) that can aid an application for opening/placing it initially. But all that matters is pixel dimensions and the above math.

 

Mike

 

so, if i want large image, i can only set the size?

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If I am making a design that is intended for output to an image type (versus a vector format) I usually make the design at 100% of the required size, then export to whatever type of file is desired.

 

It's an old habit. I have no idea of how well Affinity Designer upsamples to a larger size than as designed. Give it a try. Let me know how well it works and then we'll both know.

 

You can set the DPI at export.


My computer is a nothing-special Toshiba laptop with unremarkable specs running Windows 10 64-bit.

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The DPI (Dots Per Inch, sometimes called PPI, Pixels Per Inch) combined with the physical dimensions of the page determine how many pixels are exported. e.g. If you have a 6"x4" page, at 300DPI, that will equate to an exported pixel size of 1800x1200 (6x300 by 4x300).

 

Assuming you keep the physical dimensions of the page the same, changing the DPI should affect the file size (as it will export a different amount of pixels).

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(Dots Per Inch, sometimes called PPI, Pixels Per Inch)

 

@Mark Ingram

So do you and Serif say that DPI and PPI are the same thing? The reason I ask is I was taught that DPI has nothing to do with the resolution of an image. All DPI has to do is with printer resolution. Printers spray little dots onto the paper and the more dots it sprays, the better quality the printed image is. If you look at a printed image with a powerful magnifying glass, you can see the dots on the paper. PPI is for screen image resolution. If you zoom in on your image, you can see the little squares that are the pixels. More pixels per inch make a larger file size, but also make a higher quality image. You can have a high quality 300 PPI or 600 PPI or even 1200PPI image and print it on a poor quality 150 DPI printer and it will only have 150 DPI printed on the paper.

 

Now, when we start talking about raster vs. vector, is where I get confused.If I understand correctly, the PPI of my image doesn't matter as long as it is vector and saved as vector such as svg or pdf etc. The only time the PPI of my image matters is if I am saving it as a raster or bitmap image such as jpg or png etc. Can you clear this up or refer me to some articles that would explain it? 


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If I understand correctly, the PPI of my image doesn't matter as long as it is vector and saved as vector such as svg or pdf etc. The only time the PPI of my image matters is if I am saving it as a raster or bitmap image such as jpg or png etc. Can you clear this up or refer me to some articles that would explain it? 

Hi BobsDaubs, 

You are correct that DPI/PPI isn't relevant to vector images. Even when exporting to a bitmap, PPI doesn't affect the content; it is only used to calculate the export resolution (i.e. the number of pixels in the image).

To use Mark's example: you've created a vector image, and you want to print it on a 300 DPI printer, and you want it to fill a 6"x4" page. So you need to export image at 1800x1200. 

We save the DPI in the image's metadata as a hint to other programs that you wanted it 6"x4", but they're free to ignore this and print at a different DPI - e.g. printing at 600 DPI would will result in a 3"x2" printed image. 

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While DPI and PPI are often used interchangeably, they are NOT the same.  Pixels per inch is self evident but DPI refers to the number of dots of ink output by a printer, and they typically output four to eight dots per pixel (in each dimension).  So, if you're printing at 300 PPI you're also printing at 1200 - 2400 DPI.  Serif really should change the labels in their software to PPI - a la Photoshop et al.

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While technically correct, this strict definition of DPI is only relevant to the internal mechanics of the printer; it's not a term you'd generally find in software.

I think it's safe to assume that whenever software does mention DPI, it means PPI. 

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While technically correct, this strict definition of DPI is only relevant to the internal mechanics of the printer; it's not a term you'd generally find in software.

I think it's safe to assume that whenever software does mention DPI, it means PPI. 

Wouldn't it be better if it said PPI then?

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We use DPI because we don't know if you're going to print the document or export it as an image. If you print, then DPI = DPI, if you export, then DPI = PPI. Hence why we said the terms are used interchangeably across most software packages. 

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It may take some time to convince Microsoft to change their Explorer File > Properties > Details from displaying Horizontal and Vertical resolution in DPI, it may even be futile.

 

 

I don't have "a dog in this fight"...if I had my preference it would state reality. But spend more than five minutes dealing with the issue and it should be clear as to how/what/when the terms are independent or have identical meaning.

 

When used as a multiplier/divisor field as is the case when most applications resample, I cannot think of a better term. (Which I also do not like.)

 

post-255-0-51849600-1470922934_thumb.png

 

Windows displays images' properties properly. If there is info in the DPI metadata, it includes it, if not, it is excluded. In all cases it displays the pixel info.

 

Photoshop prior to Adobe's ownership is what started the confusion between dpi and ppi if I recall. It is carried into today.

 

Mike


My computer is a nothing-special Toshiba laptop with unremarkable specs running Windows 10 64-bit.

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We use DPI because we don't know if you're going to print the document or export it as an image. If you print, then DPI = DPI, if you export, then DPI = PPI. Hence why we said the terms are used interchangeably across most software packages. 

It doesn't matter whether you're printing or exporting - it's PPI in both cases.  I don't know what Photoshop called it before Adobe, but they call it PPI now.

 

 

http://www.andrewdaceyphotography.com/articles/dpi/

 

https://99designs.co.uk/blog/tips-en-gb/ppi-vs-dpi-whats-the-difference/?lang=en-gb?lang=en-gb

 

https://imagescience.com.au/knowledge/the-difference-between-ppi-and-dpi

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The first article is full of half-truth and perpetuates the confusion. I didn't look at the rest.

 

With a vector/illustration application such as AD is, I would say all this is much ado about nothing. With a photo/image manipulation application I would say it is more relevant to have more realistically consistent terminology.

 

It all goes back to this for me: The DPI field (two-bytes in the header if I recall) has nothing to do with resolution. It is merely an aid to placing the image in another application. Ultimately all that matters is the number of pixels spread across X amount of space.

 

Does it really matter?

 

PS perpetuated this myth for many versions after Adobe bought it and from what I can recall the last time I had an active subscription, it really isn't much more clear--as is evident by recurring posts on the Adobe forums.


My computer is a nothing-special Toshiba laptop with unremarkable specs running Windows 10 64-bit.

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I don't suppose it matters at all, except perhaps to the pedants among us.  I only entered this discussion because of the incorrect and potentially misleading (in my opinion) comments and answers given to the OP.  The bottom line is that the PPI you set in a document simply determines the size of the print, and is used as input by the printer for that purpose only.  The DPI (printer output) determines the quality of that print and is set by the printer depending on the quality setting you choose - high quality will get a high DPI and draft will get a low one, with various settings in between, and it has no relationship whatsoever to the PPI.

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Well, as long as we are being pedantic...

 

Neither PPI nor the DPI of the file is used by any printer for the print process proper. The print device is just interpolating the number of pixels into its own printer dots to the fixed size it is being fed, be it a direct print or to film (or CTP). Nor does either one determine the size of the print. Nor does either determine the quality of the print.

 

Resolution is determined by the placement size--i.e., the effective resolution. But even saying that can obviate the fact that this also does not determine the quality of the print, only its size on the printed page (assuming no scaling, that is).

 

DPI absolutely comes into play with any application that uses that field to initially place the file. It's just dumb math that an application uses without any thought of the intention of the user. (Again, assuming one simply places the file without drawing out the image frame.) However, the DPI field in the image means nothing as regards the quality of the print.

 

Like I said, I'm being pedantic.


My computer is a nothing-special Toshiba laptop with unremarkable specs running Windows 10 64-bit.

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Like I said, I'm being pedantic.

If you want to get really, really pedantic about it, you could argue that the only time PPI has any unambiguous  physical meaning is when referring to the pixels of a computer or TV display, or the sensor elements of a camera ... & even then you are probably talking about triads or other sub-pixel elements.

 

Technically, a "pixel" is defined no more precisely than as a "picture element" (thus the name), so it really isn't any less ambiguous or more context-insensitive a term than "dot."


Affinity Photo 1.6.7 & Affinity Designer 1.6.1; macOS High Sierra 10.13.5 iMac (27-inch, Late 2012); 2.9GHz i5 CPU; NVIDIA GeForce GTX 660M; 8GB RAM
Affinity Photo 1.6.7.76 & Affinity Designer 1.6.0.35 for iPad; 6th Generation iPad 32 GB; Apple Pencil; iOS 11.4.1

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Well, R, a pixel has an exact meaning. What it doesn't have is a pretermined (or, absolute) size. Which, again, is where effective resolution comes into play.

 

If we're talking printer dot, then we need to consider the matrix that makes up the series of dots that fit into the grid the printer resolves the pixels to...


My computer is a nothing-special Toshiba laptop with unremarkable specs running Windows 10 64-bit.

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I have the solution to all of the DPI/PPI confusion!

 

Since "pixel" is an ambiguous term, I propose coining a new term that makes that explicit, the Ambiguous Picture Element, or "APE" for short.

 

Thus, with the addition of only two characters all DPI or PPI references can be replaced with the all-purpose "APEPI" one (pronounced as "appey"or "eppey" as you prefer). Problem solved!

 

So, can I count on all of you voting for me in the upcoming election for president of the Pendants Club?  :lol:


Affinity Photo 1.6.7 & Affinity Designer 1.6.1; macOS High Sierra 10.13.5 iMac (27-inch, Late 2012); 2.9GHz i5 CPU; NVIDIA GeForce GTX 660M; 8GB RAM
Affinity Photo 1.6.7.76 & Affinity Designer 1.6.0.35 for iPad; 6th Generation iPad 32 GB; Apple Pencil; iOS 11.4.1

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